1. Field of the Invention
The present invention relates to a method of laminating a plastic film and shaped metal substrates. More particularly, it relates to a novel process, which can be applied for a mass production, for preparing valuable laminated shaped metal substrates including a plastic film having no defect or crease by melt-compressing the same between a pair of rolls which comprises at least one roll having a specific hollow.
2. Description of the Prior Art
Previously, coatings of a plastic on a metal substrate for imparting characteristics of anticorrosion, electric insulation, ornament, non-tacky and low friction have been applied in various fields. Various methods have been proposed for coating on metal plates, for example, the dispersion coating method using an aqueous or organic dispersion of plastic resin, the powder coating method using powdery plastic resin and the film laminating method coating a film of plastic resin have been proposed.
However, these conventional methods have certain disadvantages for a mass production of laminated products of shaped substrates such as discs.
The dispersion coating methods and powder coating methods can be applied for the mass production lines and these methods have been practically applied, however in order to form pin-holeless coated film, it is necessary to form thick coated film which is disadvantageous from an economical viewpoint. In order to form smooth coated film having uniform thickness, it is necessary to precisely control the coating operation and the curing operation whereby a complicated operation is disadvantageously required. In the case of the powder coating method, it is difficult to attain uniform coloring when an additive such as a pigment is simultaneously coated.
These disadvantages may be overcome by employing the film laminating method. When a film is laminated on a continuous ribbon type metal plate, no trouble occurs. However, in mass production of the shaped metal substrates, the following problems arise.
When the lamination is carried out by using a flat press machine, it is difficult to attain the lamination of thin film, productivity is remarkably low and the method is not applicable for mass production. When the lamination is carried out by the method of melt-compressing the film and the metal substrate between a pair of rolls which is usually employed for the lamination of a continuous ribbon type metal plate, the surfaces of the rolls are damaged by the edges of the shaped substrates. When the film, especially a thin film, is compressed on the substrate by the rolls having the defect, the same form of defect is caused on the laminated film to deteriorate the value of the laminated products. When a cookpot is prepared by a deep drawing, the disadvantages of peeling-off and damage to the film are caused at the defective part. When the shaped metal substrate has the shape of a circle, ellipsoid or triangle which contacts with the rolls in different widths, a crease is formed at a part of the laminated film in the conventional roll laminating method. The crease part is not bonded firmly on the metal substrate. When a cookpot is prepared by deep drawing the laminated metal substrate, the disadvantages of corrosion of the metal substrate and peel-off of the laminated film occur and the appearance of the value of the resulting product is inferior.